Air Leak?

Hi folks,

I inherited my grandparents home, which includes a 16x32 in ground pool. I seem to be getting some air in the system, mostly seen when I am vacuuming out the pool. I have recently (last week) replaced the mulitport valve on top of the sand filter. Also, I have replaced the gasket on the top of the pump. (where the other debris basket sits in)

The pressure gauge consistently reads about 12 psi when running in filter mode. You can see a few bubbles during normal operation, but when the vac or the navigator are hooked up, the bubbles get worse. Actually, there doesn't seem to be enough suction to run the navigator at all.

It's a Hayward super pump. I forget the model of the new multiport valve, but it replaced a Hayward sp711-13. (going off memory on that model #)

Any ideas of where I may be getting air? I don't seem to be losing any water.

Thanks!!!